A fastener includes a rod and a sleeve. The rod has a flat top for depression and a rod body extending downwardly from the flat top. The upper end of the rod body is provided with a circular groove. The sleeve is formed with a through hole and a flange close to its upper end. The inner side of the sleeve is provided above the flange with a first engaging section engageable with the circular groove of the rod. The sleeve is provided with a second engaging section below the flange and a third engaging section at the lower end thereof. By means of the engagement between the circular groove of the rod and the first engaging section of the sleeve, the rod will be prevented from detaching from the sleeve. The second and third engaging sections are used for preventing the fastener from disengaging from a workpiece.